1. Field of the Invention
The invention relates to an apparatus for the production of a cold, HF-excited plasma under atmospheric pressure conditions, comprising a metal housing that functions as a grounded electrode, in the region of the exiting plasma, in which housing an HF generator, an HF resonance coil having a ferrite core suitable for the high frequency, an insulation body that functions as a gas nozzle, as well as a high-voltage electrode mounted in the insulation body are disposed in such a manner that the process gas flows around and through them. In a preferred embodiment, the apparatus comprises an electrically conductive removable cap that has a slit or a hole in the front region. The invention can advantageously be used for plasma treatment of materials for cosmetic and medical purposes. The invention makes it possible to guarantee adherence to the guidelines of electromagnetic tolerance (EMT) by means of the integration of plasma nozzle and required control electronics into a miniaturized hand-held device or by means of the use of a short high-voltage cable, and to minimize the lost power and thereby to implement mobile use.
2. Discussion of the Background
Low-temperature plasmas have already been used for quite some time for treatment of surfaces for the purpose of surface activation, etching, polymerization, layer deposition, cleaning, as well as germ reduction. At first, low-pressure plasmas in which the reactive species required for the processes can be produced, to a defined extent, by means of the selection of suitable process parameters, were primarily used for this purpose. Because low-pressure plasmas are unsuitable for numerous industrial processes both for cost reasons and for process technology reasons, alternative plasma methods were developed that work at atmospheric pressure, are therefore significantly more cost-advantageous, and can be integrated into corresponding production lines more easily. One possibility for achieving the homogeneity of the plasmas required for the ability to use atmospheric-pressure plasma methods consists in producing a plasma jet outside the discharge space, by means of a targeted disturbance of the working gas (process gas).
Applications of such jet plasmas are described in numerous patent documents. In the unexamined published patent application DE 37 33 492 A1, for example, an apparatus for production of a jet plasma is described, in which a gas stream is passed through a corona discharge segment between a rod-shaped inner electrode and a pipe-shaped outer electrode. The method described in the patent document DE 195 32 412 C2, for plasma treatment of surfaces, is based on the production of a plasma jet by means of a strong gas stream that is passed through an arc discharge segment. In this connection, various types of feed of the electrical energy can be used for production of the atmospheric-pressure discharges. For example, in the patent documents U.S. Pat. No. 6,194,036 B1 and U.S. Pat. No. 6,262,523 B1, as well as in the patent application US 2002/122896 A1, for example, arrangements are described that are based on HF excitation of atmospheric-pressure plasmas. In the sector of medicine, special HF-excited plasmas have already been used for many years for coagulation (argon plasma coagulation: U.S. Pat. No. 4,781,175 A, U.S. Pat. No. 4,060,088 A, DE 195 13 338 A1) and for HF surgery. However, in this sector, there have also been numerous more recent developments, which pursue the goal of using plasmas of this type also, for example, for coating implants to increase their biocompatibility, as well as for controlling cell adhesion on surfaces (Ohl A., Schröder K.: Plasma assisted surface modification of biointerfaces. In: Hippler R., Kersten H., Schmidt M., Schoenbach K. H. (ed.). Low Temperature Plasmas, Vol. 2. 803-820. Wiley-VCH, Weinheim 2008), for antimicrobial decontamination of surfaces (R. Brandenburg et al.: Contrib. Plasma Phys. 2007, 47, (1-2), 72-79), as well as for treatment of biological cells and tissue (I. E. Kieft et al.: IEEE Transactions on Plasma Science 2005, 33, (2), 771-775).
The invention refers to an apparatus of the type described in the patent document of the applicant, “DE 10 2006 019 664 A1”. There, an easy to handle HF plasma nozzle is described, in which it is possible to do without an HF adaptation network in the form of a separate matchbox, because of the special construction. In this way, it is possible to implement an easy to handle construction of the HF plasma nozzle, which can be guided both manually and by robots.
The connection of plasma nozzle and HF generator by means of a longer cable leads to the result that the values of the electromagnetic interference radiation that occur during operation of an apparatus according to the state of the art generally exceed the limit established by the European guidelines for electromagnetic tolerance (EMT). Apparatuses of this type cannot be used without greater technical effort for ensuring adherence to these guidelines. This means that their use is restricted to applications in industrial facilities that are shielded toward the outside by means of special measures with regard to electromagnetic interference radiation. For mobile use in public areas, for example for medical, dental or cosmetic purposes, use of this apparatus is only possible if it meets the EMT requirements. It is the task of the invention to implement a plasma tool on the basis of a cold, HF-excited plasma jet that satisfies these EMT requirements and thus is suitable for mobile use in the sectors of medicine, dentistry and cosmetics. Another task consists in working in particularly gentle manner in more sensitive regions of the body. During plasma treatment, reactive species (radicals) and radiation (VUV/UV), which are important for the treatment effect, are particularly produced. For another thing, the plasma is heated as the result of loss processes, and the temperature at the tip amounts to about 50° C., which must be considered “cold” under plasma conditions. However, when used on human skin, permanent local treatment of the skin with a plasma at this temperature leads to local burns. In order to avoid such burns, the plasma is currently moved over the location to be treated at a specific speed.
Further irritation (irritation) of the skin, which expresses itself in unpleasant “tingling,” is caused by the electrical current that flows from the high-voltage electrode (3) to the skin surface, by way of the conductive plasma. Normally, this is not a problem and more or less tolerable. In more sensitive regions of the body, such as in the oral cavity (in the case of treatment of the gums), for example, this is painful and cannot be defended.